1. Field of the Invention
The present invention relates to an inertial instrument and more specifically pertains to vibrating accelerometers used as multi-sensors for measuring linear acceleration and rate of rotation of a moving body.
2. Description of Prior Art
Gyroscopes are well known for use as angular velocity and acceleration sensors for sensing angular velocity and acceleration which information is necessary for determining location, direction, position and velocity of a moving vehicle.
The present invention utilizes two masses in tandem, a dither mass and a proof mass, or pendulum. Each mass has only a single degree of freedom. It is desired to have the dither mass move along an axis that is parallel to the plane of the housing. The driving forces on the dither mass causing its vibration do not act directly on the pendulum. These forces, however cause the dither mass to move out of the plane of the housing due to dither beam misalignments. This out-of-plane motion generates error signals which are in quadrature with the signals generated by rate inputs. Therefore, a high degree of phase discrimination is required to separate the rate signal from the quadrature signal. This invention uses a new quadrature nulling technique which eliminates the requirement for accurate phase and relaxes control of the dither beam alignment tolerances which generate out of plane motion. The present invention applies vibration driving signals to the dither mass to vibrate the dither mass and the proof mass at a combined resonant frequency, and applies a restoring force to the proof mass which is in phase with its dithered displacement. In an alternate embodiment, vibration driving signals are applied to the dither mass to vibrate the dither mass and proof mass which are in an X-Y plane at a combined resonant frequency about the Z axis of the X-Y plane. A restoring torque is applied to the proof mass which is in phase with its dithered displacement.